The present application is a continuation-in-part of application Ser. No. 08/029,762 and which was filed on Mar. 11, 1993, now abandoned.
1. Field of the Invention
The present invention relates to an improved orthodontic appliance, and more particularly, to a composition which may be applied to the orthodontic appliance thereby increasing the strength of same, and, simultaneously providing a durable and substantially transparent finish or coating which imparts improved aesthetic and other performance characteristics to the orthodontic appliance.
2. Description of the Prior Art
The prior art is replete with numerous examples of improved orthodontic appliances which have been utilized by clinicians in the treatment of various orthodontic maladies. As a general matter, manufacturers of orthodontic appliances have endeavored through the years to produce aesthetically pleasing appliances, but their efforts have met with only limited success. For example, and while many of the orthodontic products which have been introduced have had varying degrees of success, they have each had shortcomings which have detracted from their usefulness. These deficiencies in the prior art devices have often manifested themselves in increased amounts of clinician's time, or otherwise resulted in broken or damaged appliances, and on some occasions, patient trauma.
Examples of various orthodontic appliances which have been introduced to address various aesthetic considerations have included so-called "pure" polycarbonate brackets. While the aesthetic considerations of these types of brackets were generally quite improved, in relative comparison to metal brackets, for example, they have not been as successful as manufacturers once hoped. In particular, pure polycarbonate brackets are difficult to adhesively bond to a patients teeth and have, from time to time, detached or debonded from the patients teeth due to occlusal or masticatory forces. Additionally, such brackets or appliances are somewhat weak thereby causing the appliances to fail or otherwise distort over time. Moreover, these same brackets or appliances are sometimes chemically reactive with the fluids found in the patients' oral cavity and therefore may tend to stain or otherwise discolor over time.
In contrast to the "pure" polycarbonate brackets noted in the paragraph above, glass-filled polycarbonate is much stronger, relatively speaking, than pure polycarbonate. However, this material suffers from the same problems as pure polycarbonate with respect to bonding and staining. However, glass-filled polycarbonate has excellent aesthetic qualities inasmuch as that it normally blends in quite well with the natural tooth structure.
Other materials have been employed in the manufacture of orthodontic appliances such as LCP, polyetherimide, PET, PES, and PS, however, these materials have been less than ideal due to a lack of strength or bonding difficulties. Furthermore, these same materials are not translucent or are colored and therefore, their aesthetic value is considered somewhat marginal.
Other materials which have been utilized in combination with glass-filled polycarbonates have included assorted metals. For example, orthodontic appliances have been manufactured which have included a stainless steel insert. While these devices have operated with some degree of success, they have not been well received from an aesthetic view point because the gray color of the metal may often be seen through the bracket. Also, the same orthodontic appliances have exhibited tie wing strength problems and also some propensity for failure as when the metal slots are pulled out of the bracket. These brackets are similarly difficult to bond in view of the presence of the polycarbonate.
Another material utilized in the manufacture of orthodontic appliances is polycrystalline .alpha.-alumina. Polycrystalline .alpha.-alumina is generally considered to have excellent aesthetic characteristics, that is, it blends in well with a patients natural tooth structure, however, orthodontic appliances manufactured with such materials have been less than satisfactory due to their propensity to fracture, especially in the tie-wing or arch slot areas. Additionally, appliances utilizing this same material, while acceptable from an aesthetic standpoint are relatively costly to produce, and have exhibited other detrimental performance characteristics such as increased friction in the arch slot areas of a bracket. Many of the same problems related to polycrystalline .alpha.-alumina are present when utilizing single crystal .alpha.-alumina. However, when single crystal .alpha.-alumina is employed in the manufacture of brackets, upon failure, the bracket tends to shatter, as opposed to fracturing.
Other attempts in the art to address these same aesthetic considerations have included the application of polymer or electrostatic pigment coatings on orthodontic appliances. These coatings have been less than satisfactory, however, in view of problems attendant to slot tolerances. Additionally, these coatings have a propensity for chipping off. Furthermore, these coatings are non-translucent and, if the associated bracket is one which includes a metal slot, then, in that event, the gray colored metal may be seen, on occasion, underneath the coating once the coating has chipped off, or otherwise worn away. Finally, ceramic materials have been widely used for orthodontic appliances. However, these materials have many disadvantages including difficulties in bonding, and extreme brittleness under some conditions. Furthermore, such brackets potentially can abrade the enamel of a patients teeth and normally must be made larger than a corresponding metal bracket for similar strength.
Therefore, it has long been known that it would be desirable to have an improved orthodontic bracket which has acceptable aesthetic qualities, and which further avoids the shortcomings attendant with the prior art materials and practices.